A growing bioeconomy requires increasing amounts of biomass from industrial crops for bioenergy and bio-based products. There is much discussion about how industrial crop cultivation could promote social-ecological outcomes such as environmental protection, biodiversity conservation, climate change adaptation, food security, greenhouse gas mitigation, and landscape appearance.
In Germany, maize is the main industrial crop used as a biogas substrate to provide heat and electricity, because of its high biogas yield potential. However, maize is associated with problems such as soil erosion, biodiversity loss, an increase in wild boar populations, and lowered landscape diversity. The cultivation of perennial wild plant mixtures (WPMs) addresses many of these problems. Despite being less developed than maize, WPM cultivation has received notable attention among scientists in Germany over the past decade.
I’ve recently published a review article in Advanced Sustainable Systems that provides an overview of the first experiences with WPM cultivation from scientists and farmers. WPMs are perennial cropping systems that can provide both biomass for biogas production and food and shelter for pollinators and open land animals. WPMs offer a dynamic and diverse species composition of flowering and predominantly wild plant species, which increases both agrobiodiversity and landscape appearance compared to conventional biogas crops.
Consequently, WPM cultivation offers great social-ecological advantages over conventional biogas cropping systems, but the average biogas yield of WPMs is still significantly lower. This results in negative land use change effects, i.e., more land is needed to produce the same amount of bioenergy (in the form of biogas and heat) as, for example, in the cultivation of maize.
However, the continued improvement and practical application of existing WPM cultivation systems can still be recommended. This is because it is a very young cultivation system in terms of its development status, and the biomass yield potential of WPMs can already reach a level of competitiveness with conventional biogas crops such as maize under certain conditions, according to several studies. An adaptation of the WPM cultivation system could help improve the biomass yield potential (the most important determinant for the biogas yield) especially on marginal agricultural land, which must be considered to help achieve food security in the long term, because the favorable land will be kept for food crop cultivation. The potential of WPM biomass for cascade use, i.e., the successive use for bio-based products and biofuels, has not yet been investigated, but appears promising due to the lignocellulosic composition of some wild plant species comparable to common industrial crops.
Furthermore, the additional social-ecological benefits of WPM cultivation can be so significant under certain local conditions that the still relatively low economic performance of the cultivation system can be ignored. This could be, for example, in the proximity of the field to residential, recreational, or nature conservation areas. Moreover, unfavorable size/shape of the fields cultivated with food crops can make it possible to cultivate WPMs because, apart from improving the management of the remaining primary field, the species-rich WPM area increases the habitat availability for beneficial insects. And both a higher abundance and diversity of beneficial insects can help reduce the pesticide requirements of the primary field.
However, a complete replacement of the conventional biogas crops by WPMs cannot be recommended at present, because it is highly probable that the overall sustainability of the biomass supply would be significantly lower than in current circumstances due to enormous land use change effects.
Instead, a meaningful addition of WPMs to the range of conventional biogas crops can very likely enhance the overall sustainability of biogas cropping systems. Only then would it appear reasonable in the long term to cultivate biomass for bioenergy and thus, at least in the energy sector, help significantly toward achieving a transition to a fossil-free and social-ecologically sustainable bioeconomy.
Reference: M. von Cossel, ‘Renewable Energy from Wildflowers—Perennial Wild Plant Mixtures as a Social‐Ecologically Sustainable Biomass Supply System.’ Advanced Sustainable Systems (2020). DOI: 10.1002/adsu.202000037